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<br /> <br />f? <br />CO-0000906 <br />New Elk Mine Water Quality Assessment <br />The SCT for most pollutants equals the BWQ concentration plus 15 percent of the remaining <br />assimilative capacity, and is calculated by the following equation: <br />Where, <br />SCT = 0.15 x (WQS-B WQ) + B WQ <br />WQS = water quality standard (chronic standard or, in the absence of a chronic standard, <br />the acute standard) <br />ADBACs are then determined by re-calculating the mass-balance equation using the SCT in place of <br />the water quality standard, as in the following equation: <br />ADBAC = SCT x Q3 - M, X Q, <br />Q2 <br />Where, <br />Q, = Upstream low flow (I E3 or 30E3) <br />Q2 = Average daily effluent flow (design capacity) <br />Q3 = Downstream flow (Qj + Q2) <br />MI = Ambient existing water quality concentration (From Section 11) <br />SCT = Significant concentration threshold <br />For mercury, which is a bioaccumulative toxic pollutant, the ADBAC is calculated as 10% more than <br />the existing load. Because the existing load for mercury is zero, the ADBAC is also zero. <br />The SCTs and ADBACs for pollutants of concern were calculated and are set forth in Table A-9. <br />Note that SCTs and ADBACs were not determined for total recoverable iron because new or <br />increased impacts were not expected as part of this permit, as previously discussed. <br />Appendix A (wQA version 5-4(FAai-)) Page 26 of 29 Last Revised August 26, 2008